A waterjet propulsion unit for a waterborne vessel produces thrust by way of a reaction to discharge of a high speed jet stream from an engine driven pump and nozzle arrangement. A steering deflector mounted at the outlet of the nozzle can direct the stream substantially laterally in relation to the longitudinal axis of the vessel to provide steering. A reverse duct mounted astern of the steering deflector can direct the stream substantially ahead along the longitudinal axis to provide reverse. One to four or more propulsion units may be installed across the stern according to size of a particular vessel or a configuration designed for the vessel. A bow thruster may also be used to assist some manoeuvres.
Engine power levels and the reverse ducts are conventionally controlled using lever systems which vary the ahead and astern thrust of each waterjet in both magnitude and direction. A single lever often controls both the throttle and the position of the duct. With the lever in a central position the engine idles and the duct is partially down to produce zero net thrust. Moving the lever forwards or backwards initially raises or lowers the duct at constant throttle, and then opens the throttle, to create a range of thrust levels directed ahead or astern. Separate levers may also control the throttle and duct for each unit although this can be cumbersome for the operator.
Steering may be controlled in various ways. Some waterjet units have independent steering deflectors and reverse ducts, in which case the steering deflectors on all of the units in an installation are generally controlled synchronously by way of a helm wheel or steering joystick. Other units have the reverse ducts mounted on the steering deflectors and their operation is not independent, in which case the steering deflectors on each of the waterjets in an installation may not be controlled synchronously. The control requirements of these two alternative systems are generally different.
Rotation and forward or backward translation of a vessel having multiple waterjet units is usually straightforward using existing control systems. However, a sideways manoeuvre into a berth for example, can be awkward or counterintuitive even for experienced operators. U.S. Pat. No. 5,031,561 describes a relatively complex system for a vessel having reverse ducts mounted on the steering deflectors. The system involves two modes in which the steering deflectors are operated synchronously when underway but differentially for many manoeuvres.